Procelewska Joanna, Zahl Achim, Liehr Günter, van Eldik Rudi, Smythe Nicole A, Williams B Scott, Goldberg Karen I
Institute for Inorganic Chemistry, University of Erlangen-Nürnberg, Germany.
Inorg Chem. 2005 Oct 31;44(22):7732-42. doi: 10.1021/ic050478+.
Cationic complexes of the type fac-[(L(2))Pt(IV)Me(3)(pyr-X)][OTf] (pyr-X = 4-substituted pyridines; L(2) = diphosphine, viz., dppe = bis(diphenylphosphino)ethane and dppbz = o-bis(diphenylphosphino)benzene; OTf = trifluoromethanesulfonate) undergo C-C reductive elimination reactions to form [L(2)Pt(II)Me(pyr-X)][OTf] and ethane. Detailed studies indicate that these reactions proceed by a two-step pathway, viz., initial reversible dissociation of the pyridine ligand from the cationic complex to generate a five-coordinate Pt(IV) intermediate, followed by irreversible concerted C-C bond formation. The reaction is inhibited by pyridine. The highly positive values for DeltaS()(obs) = +180 +/- 30 J K(-1) mol(-1), DeltaH(obs) = 160 +/- 10 kJ mol(-1), and DeltaV()(obs) = +16 +/- 1 cm(3) mol(-1) can be accounted for in terms of significant bond cleavage and/or partial reduction from Pt(IV) to Pt(II) in going from the ground to the transition state. These cationic complexes have provided the first opportunity to carry out detailed studies of C-C reductive elimination from cationic Pt(IV) complexes in a variety of solvents. The absence of a significant solvent effect for this reaction provides strong evidence that the C-C reductive coupling occurs from an unsaturated five-coordinate Pt(IV) intermediate rather than from a six-coordinate Pt(IV) solvento species.
fac-[(L(2))Pt(IV)Me(3)(pyr-X)][OTf]类型的阳离子配合物（pyr-X = 4-取代吡啶；L(2) = 二膦，即dppe = 双（二苯基膦基）乙烷和dppbz = 邻双（二苯基膦基）苯；OTf = 三氟甲磺酸盐）发生C-C还原消除反应，生成[L(2)Pt(II)Me(pyr-X)][OTf]和乙烷。详细研究表明，这些反应通过两步途径进行，即吡啶配体首先从阳离子配合物中可逆解离，生成五配位的Pt(IV)中间体，随后是不可逆的协同C-C键形成。该反应受吡啶抑制。ΔS()(obs) = +180 +/- 30 J K(-1) mol(-1)、ΔH(obs) = 160 +/- 10 kJ mol(-1)和ΔV()(obs) = +16 +/- 1 cm(3) mol(-1)的高度正值可以用从基态到过渡态时显著的键断裂和/或从Pt(IV)到Pt(II)的部分还原来说明。这些阳离子配合物为在各种溶剂中对阳离子Pt(IV)配合物的C-C还原消除进行详细研究提供了首个机会。该反应不存在显著的溶剂效应，这有力地证明了C-C还原偶联是从不饱和的五配位Pt(IV)中间体发生的，而不是从六配位的Pt(IV)溶剂化物物种发生的。
